• Journal of the Korean GEO-environmental Society
• /
• v.13 no.10
• /
• pp.25-32
• /
• 2012

The application of electrical resistivity, which is related to charge mobility, has increased in the field of geotechnical engineering for the detection of underground cavern, faults and subsurface pollution level. The purpose of this study is to investigate the variation of electrical resistivity due to temperature change. Sand-silt mixture specimens prepared in the square freezing nylon cell are frozen in the frozen chamber. Four electrodes are attached on the four side walls of the freezing cell for the measurement of electrical resistance during temperature change. Electrical resistances of sand-silt mixtures with different degrees of saturation (0%, 2.5%, 5%, 10%, 20%, 40%, 60% and 100%) are measured as the temperature of specimens decrease from $20^{\circ}C$ to $-10^{\circ}C$. The electrical resistances determined by Ohm's law are transformed into the electrical resistivity by calibration. Experimental results show that the higher degree of saturation, the lower electrical resistivity at $20^{\circ}C$. Electrical resistivity gradually increases as the temperature decrease from $20^{\circ}C$ to $0^{\circ}C$. For the specimens with the degree of saturation of 15% or higer, electrical resistivity dramatically changes near the temperature of $0^{\circ}C$. In addition, very high electrical resistivity is observed regardless of the degree of saturation if the specimens are frozen. This study provides the fundamental information of electrical resistivity according to the soil freezing and temperature change demonstrates that electrical resistivity be a practical method for frozen soil investigation.

• Polymer(Korea)
• /
• v.24 no.4
• /
• pp.529-537
• /
• 2000

The effects of the gel content on the cell structures of PP sheets by using an electron-curing system were investigated. Three extruded PP sheets crosslinked by three different doses were used for the batch foaming process with the supercritical state $CO_2$. Experiments were also performed in order to study the effects of the gel content, saturation pressure and temperature on cell structures. Then foaming conditions, such as temperature and duration of time, were changed. The amount of gas absorbed into PP samples was not affected by gel contents and the operating condition of saturation pressure, which was higher than 2000 psi. The foam cells of PP with a low gel content grew irregularly at a higher foaming temperature and for a longer duration of foaming time. However, PP samples with high gel content showed even cell structures and narrow tell size distributions under the severe conditions of high foaming temperatures and long duration of foaming time.

• Proceedings of the SAREK Conference
• /
• 2006.06a
• /
• pp.68-73
• /
• 2006

The present paper deals with an experimental study of boiling heat transfer characteristics of R-290, and is focused on pressure gradient and heat transfer coefficient of the refrigerant flow inside horizontal smooth minichannel with inner diameter of 3.0 mm and length of 2000 mm. The direct heating method applied for supplying heat to the refrigerant where the test tube was uniformly heated by electric current which was applied to the tube wall. The experiments were conducted with R-290 with purity of 99.99% at saturation temperature of 0 to $10^{\circ}C$. The range of mass flux is $50{\sim}250kg/m^2s$ and heat flux is $5{\sim}20kW/m^2$. The heat transfer coefficients of R-290 increases with increasing mass flux and saturation temperature, wherein the effect of mass flux is higher than that of the saturation temperature, whereas the heat flux has a low effect on increasing heat transfer coefficient. The significant effect of mass flux on heat transfer coefficient is shown at high quality, the effect of heat flux on heat transfer coefficient at low quality shows a domination of nucleate boiling contribution. The heat transfer coefficient of the experimental result was compared with six existing heat transfer coefficient correlation. Zang et al.'s correlation(2004) gave the best prediction of heat transfer coefficient.

• Journal of Magnetics
• /
• v.19 no.1
• /
• pp.5-9
• /
• 2014

The amine functionalized $CoFe_2O_4$ nanoparticles were prepared by thermal decomposition method at reflux temperatures $160^{\circ}C$ and $172^{\circ}C$. The obtained $CoFe_2O_4$ nanoparticles at $160^{\circ}C$ reflux temperature show aggregation free poly-dispersed nanoparticles in 4-15 nm range. In an elevated reflux temperature of $172^{\circ}C$, $CoFe_2O_4$ show aggregated poly-dispersed nanoparticles in the size range of 20-46 nm. The saturation magnetization value at 300 K exhibited 51 emu/g at reflux temperature of $160^{\circ}C$. However, the sample synthesized at an elevated temperature of $172^{\circ}C$ has shown a coercive field value of 560 Oe with saturation magnetization of 68 emu/g.

• Journal of the Optical Society of Korea
• /
• v.20 no.5
• /
• pp.593-600
• /
• 2016

Operation properties, such as output power, beam radius, and crystal temperature rise were investigated in a diode-pumped edge-cooled monolithic Yb:YAG laser with ~ 4 W pumping level. The output power showed saturation behavior because of severe temperature rise and poor spatial overlapping between pump beam and lasing mode. Face cooling geometry by using a sapphire plate was also investigated. No apparent saturation behavior in output power was observed due to the reduced temperature rise, which could be attributed to efficient heat removal through the crystal-sapphire interface.

• Journal of Power System Engineering
• /
• v.11 no.1
• /
• pp.63-69
• /
• 2007

The evaporation pressure drop of $CO_2$ (R-744) in a horizontal tube was investigated experimentally. The main components of the refrigerant loop are a receiver, a variable-speed pump, a mass flow meter, a pre-heater and an evaporator (test section). The test section consists of a smooth, horizontal stainless steel tube of 4.57 mm inner diameter. The experiments were conducted at saturation temperature of $-5^{\circ}C\;to\;5^{\circ}C$, and heat flux of 10 to $40kW/m^2$. The test results showed that the evaporation pressure drop of $CO_2$ are highly dependent on the vapor quality, heat flux and saturation temperature. The measured pressure drop during the evaporation process of $CO_2$ increases with increased mass flux, and decreased saturation temperature. The evaporation pressure drop of $CO_2$ is much lower than that of R 22. In comparison with test results and existing correlations, the best fit of the present experimental data is obtained with the previous correlation. But existing correlations failed to predict the evaporation pressure drop of $CO_2$. Therefore, it is necessary to develop reliable and accurate predictions determining the evaporation pressure drop of $CO_2$ in a horizontal tube.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.16 no.8
• /
• pp.744-751
• /
• 2003

Co-Pd alloy thin films prepared by a DC-sputter that have self-organized nano structure(SONS), are promising for high-density information storage media in information era. We prepared the samples by varying Pd contents of 0~8.1 wt% at the substrate temperatures of room temperature (RT) and 200 $^{\circ}C$, respectively Microstructure and Pd contents of the Co$_{1-x}$ Pd$_{x}$ films are probed by a scanning electron microscope (SEM), a transmission electron microscope (TEM) and an energy dispersive spectrometer (EDS). We also investigated the saturation magnetization (Ms), remanence and coercivity of the Co$_{1-x}$ Pd$_{x}$ films. Surface roughness are measured by an atomic force microscope (AFM). We revealed that self-organized nano size Co-enriched phase and Pd-enriched phase existed with Pd contents at the substrate temperatures of RT and 20$0^{\circ}C$ through microstructure characterization. SONS helped to keep the saturation magnetization and enhance the perpendicular anisotropy with Pd contents. Out result implies that we may tune the perpendicular magnetic properties with keeping the saturation magnetization by varying substrate temperatures and Pd contents for high density magnetic recording.rding.

• Proceedings of the KSME Conference
• /
• 2004.04a
• /
• pp.1340-1345
• /
• 2004

Convective boiling heat transfer coefficients of R-22 were obtained in a flat extruded aluminum tube with $D_h=1.41mm$ . The test range covered mass flux from 200 to 600 $kg/m^2s$, heat flux from 5 to 15 $kW/m^2$ and saturation temperature from $5^{\circ}C$ to $15^{\circ}C$ . The heat transfer coefficient curve shows a decreasing trend after a certain quality(critical quality). The critical quality decreases as the heat flux increases, and as the mass flux decreases. The early dryout at a high heat flux results in a unique 'cross-over' of the heat transfer coefficient curves. The heat transfer coefficient increases as the mass flux increases. At a low quality region, however, the effect of mass flux is not prominent. The heat transfer coefficient increases as the saturation temperature increases. The effect of saturation temperature, however, diminishes as the heat flux decreases. Both the Shah and the Kandlikar correlations underpredict the low mass flux and overpredict the high mass flux data.

• International Journal of Air-Conditioning and Refrigeration
• /
• v.12 no.3
• /
• pp.148-157
• /
• 2004

Convective boiling heat transfer coefficients of R-22 were obtained in a flat extruded aluminum tube with $D_h=1.41mm$. The test range covered mass flux from 200 to $600kg/m^{2}s$, heat flux from 5 to $15kW/m^2$ and saturation temperature from $5^{\circ}C\;to\;15^{\circ}C$. The heat transfer coefficient curve shows a decreasing trend after a certain quality (critical quality). The critical quality decreases as the heat flux increases, and as the mass flux decreases. The early dryout at a high heat flux results in a unique 'cross-over' of the heat transfer coefficient curves. The heat transfer coefficient increases as the mass flux increases. At a low quality region, however, the effect of mass flux is not prominent. The heat transfer coefficient increases as the saturation temperature increases. The effect of saturation temperature, however, diminishes as the heat flux decreases. Both the Shah and the Kandlikar correlations un-derpredict the low mass flux and overpredict the high mass flux data.

• Journal of the Korean Ceramic Society
• /
• v.37 no.6
• /
• pp.530-536
• /
• 2000

During the grain growth of the PZT thin films by selective nucleation method using PZT seed, it was found that the grain size was saturated with the annealing temperature. The saturation of grain size was analyzed by the interfacial energy which appeared during the crystallization. The factors affecting the saturation of grain size were found to be the interfacial energy between perovskite phase and pyrochlore phase, and PZT thin film and the bottom Pt electrode. When the ion damage was introduced to the grain-size saturated PZT thin films, further lateral growth was observed. Pt bottom electrode thickness was changed to control the interfacial energy between the PZT thin film and the Pt bottom electrode. When Pt thickness was increased, the grain size was also increased, because the lattice parameter of Pt films was increased with the thickness of the Pt films. The incubation time of nucleation was increased with the amount of the ion damage on the Pt films.